In the past commercial, industrial, or residential forced-air gas pilot ignition furnaces having 24Vac control circuits have burned gas continuously during the heating portion of the operating cycle. A typical heating cycle begins when the temperature of the unit, such as a house, for example, falls below the set temperature of a thermostat. At this point the thermostat sends a signal to the furnace to turn on the gas burner. The gas burner burns continuously to heat up the heat exchanger of the furnace. Then the blower fan turns on to draw cold air from the house through the heat exchanger to be heated and returned to the house. This heating process continues until the temperature of the house rises above the set temperature of the thermostat. At this point, the thermostat sends a signal to the furnace to turn off the gas burner.
During the heating cycle, the burner is continuously burning the gas. Thus, the heat exchanger is continuously heated right up to the turn off point. The temperature of the heat exchanger thus rises above the point that the cold air being drawn through the heat exchanger can maintain the temperature of the heat exchanger at an efficient operating level. When this happens, the excess heat is vented out via a chimney and wasted. Applicant has discovered that up to about 30 percent of the gas burning during the furnace on time is wasted.
Known efforts to overcome the above described furnace heat exchanger overheating problem and conserve gas has resulted in the development of a pulsed type fuel injection system. The pulsed fuel injection system pulses a gas/air mixture into a combustion chamber for ignition by a spark plug.
Although the efficiency level of the pulsed fuel injection system is about 93 to 95 percent compared to about 70 percent for the typical gas furnace, several disadvantages attend the use of the pulsed fuel injection system. For example, the combustion products include water containing acid and toxic materials which must be disposed of in compliance with environmental protection regulations. The explosion of the combustion mixture produces noises emitted by the furnace at an objectionable level. Also, the cost of the furnace as compared to the typical furnace is increased substantially, thus requiring at least a five to eight year payback period.
Another known system developed to overcome the problem of the typical gas furnace is the electronic ignition furnace. The electronic ignition furnace is a pilotless furnace with an efficiency level of about 80 percent. Like the pulsed fuel injection furnace, the electronic ignition furnace is very expensive as compared to the typical furnace. Also, the original furnace must be removed as in the pulsed fuel injection furnace.
Another known system used to control energy is the set-back thermostat. The set-back thermostat includes a built in clock. The temperature is automatically lowered at various times such as when there is no one there or at night. The problem with this system is that the only way to lower fuel costs is to lower the temperature. Also they are battery operated, and all programming is erased if power is absent for 48 hours or longer. The set-back thermostat has a payback period of about one winter season.
One major advantage of the present gas burner furnace cotnrol invention is the increased efficiency in gas consumption. Other advantages of the invention stem from the fact that the gas burner furnace control device is an add-on device which is inexpensive, easy to install and utilizes the electrical power supply of the furnace for operation. The use of the furnace power supply eliminates the need for a battery-type power supply, typically required for electronic circuits using Vcc. The device can also be used together with the set-back thermostat to provide maximum gas furnace operation economy.